Work holder



Sept. 1, 1936. w. L. BOWER 2,@53,177

WORK HOLDER Filed Dec. 6, 1954 Patented Sept. 1, 1936 UNITED STATES PATENT OFFICE WORK HOLDER Application December 8, 1934,.801'131 No. 756,373

In Great Britain December 12,

14 Claims.

This invention relates to work holders or chucks of the type in which articles of magnetic material to be worked upon, for example to be ground, are held in position by magnetic forces. In work holders of this type as heretofore constructed the magnetic forceis produced by electro-magnets; this necessitates a supply of direct current, and this in turn frequently necessitates the provision of rectiiiers or rotary converters. The replacement of the electromagnets by permanent magnets would make the work holder independent of any source of current, eliminate the risk of an electrical breakdown and render the work holder readily transportable; in the case of rotary work holders, electrical brush gear would be eliminated and the construction thereby simplified; The use of permanent magnets for this Purpose has in fact been proposed heretofore, but in these prior proposals no means were provided to allow of the work being readily removed from the work holder, it being necessary to force the work away against the magnetic attraction.

The present invention overcomes this difliculty in that the poles of the permanent magnets are covered by separate pole pieces, which can be moved relative to the magnets so as to ensure that all or almost all the magnetic flux between adjacent magnetic poles passes through the pole pieces, when the work piece is in the normal magnetic work holding zone, so that the work piece is thereby released while it remains in such zone. Preferably pole pieces for all the magnet poles are cast into a plate of non-magnetic ferrous alloy which forms a table for the work piece; preferably also this face plate forms the cover of a casing within which the magnets are slidably arranged.

Two embodiments of the invention are shown in the accompanying drawing, in which Figure 1 is a plan view oi the preferred form of the invention; Figure 2 a section on the line A--A of Figure 1; Figure 2A is a fragmentary detail sectional view generally similar to Figure 2, but showing the magnets shifted into work releasing position; Figure 3 a section on the line B-.-B of Figure 1; while Figure 4 is a section, similar to that of Figure 2, through a modified form of the invention.

Referring first to Figures 1 to 3 of the drawing, the eight permanent magnets I are of W shape having three poles each. Each pole is covered by a separate pole piece 2 of high permeability magnetic material and all the pole pieces I 55 are cast into a face plate 3 of non-magnetic fer- 'rous alloy which forms a table for the work piece. The face plate 3 also forms the cover of a casing 4 within which the magnets i are slidably arranged. The magnets are connected together by a link i and by another link 6 to an eccentric 5 pin 1 on a shaft 8, which can be rotated by a handle 9. By turning the handle 9 the magnets are moved to the right, as shown in Figure 2A,

so that the pole pieces 2 bridge the gaps between adjacent poles, whereby almost all the magnetic 10 flux passes through the pole pieces and only a vvery small amount still passes through the work piece. The work piece can then readily be removed. In this position the pole pieces form keepers for the magnets and prevent them from is losing their magnetism.

In the construction shown in Figure 4, the' magnets are in the form of straight bars is with their north and south poles alternately uppermost and a second moveable plate'la with cast 20 in pole pieces 2a is arranged beneath the bottom ends of the magnets. The pole pieces in the bottom plate are displaced relative to the pole pieces 2 in the top plate 8, so that when the latter cover the tips of the magnets and are there- 25 by energized, the pole pieces In in the bottom plate to bridge the gaps between adjacent poles and are thereby de-energized; when the pole pieces in the top plate are de-energized, the pole pieces in the bottom plate cover the tips of the magnets and are thereby energized. The work holder thus has two opposite faces, one 01 which is always energized while the other is de-energized. In other respects this form of the invention is similar to the form shown in Figures 1 to 3 of the drawing.

What I claim and desire to secure by Letters Patent is:-

1. A magnetic work holder comprising 9. nor mally open circuit of magnetic material including permanent magnets having poles of opposite polarity separated one from the other so that, when work to be held is placed within the zone of magnetic influence of said poles, the magnetic flux passes from one pole to the other through the work, and means operable at will for estab lishlng an auxiliary circuit to shunt the field out of the work while the work remains in the normal magnetic work holding zone to substantially release the work to enable its ready removal respecting the holder.

2. A work holder for articles of magnetic material comprising a plurality of permanent magnets having poles of opposite polarity disposed adjacent to one another, a work supporting member 65 poles of diii'erent polarity arranged alternately,

a work supporting member for holding the work in the magnetic zone of influence of said poles and including a member of magnetically conducting material overlying each of said poles, and common means for effecting relative movement between all of said members and said poles to bridge adjacent poles of opposite polarity, whereby to establish a shunt magnetic circuit to shunt the field of said magnet poles out of the work and release the latter while the work remains in the normal magnetic work holding zone.

' 4. A work holder for articles of magnetic material comprising a plurality of coplanar permanent magnet poles of alternate polarity, a plate of nonmagnetic material superimposed on said poles, said plate having apertures therein in the zone of magnetic influence, members of magnetically conducting material located in said apertures, one member overlying each of said poles, and means for effecting relative movement between said poles and said plate, whereby to establish an auxiliary circuit to shunt the fleld out of the work and release the latter while the work remains in the normal magnetic work holding zone.

5. A work holder for articles of magnetic material comprising a work holding member, a plurality of permanent magnets mounted contiguous to said work holding member, magnetic conductors of high permeability mounted in said work holding member for causing flux from said magnets to flow through work laid on said member within the zone of magnetic influence, and means for effecting relative movement between said magnets and said conductors to shunt said flux out of said work while the work remains in the normal magnetic work holding zone of said magnets.

6. A magnetic chuck, comprising a magnet having at least two poles of opposite polarity disposed adjacent to each other, a member associated with said magnet adapted to hold work thereon by the magnetic attraction of said magnet when said member is in one position respecting said magnet poles, and means for moving one of the parts aforesaid relatively to the other so as to establish an auxiliary circuit to divert the flux out of the work while the work remains in the normal magnetic work holding zone, and to release said work, when the member is in another position respecting said magnet poles.

'7. A magnetic chuck, comprising means for creating a magnetic fleld, a work supporting member disposed in said magnetic held and having portions of relatively high and relatively low permeability, and means for selectively adjusting said work supporting member relatively to said magnetic field whereby to cause the magnetic flux to pass through the work on the chuck to hold said work in position to be operated upon, said means being shiftable to establish an auxiliary circuit to cause the magnetic flux to be diverted from the work while the work remains in the a,oss,117

magnetic work holding zone to release the work.

9. A magnetic chuck, comprising a permanent magnet having at least two poles of opposite polarity, a work supporting member having portions of relatively high permeability for establishing a closed magnetic circuit through the work-piece when placed in the zone of magnetic influence of said poles, whereby to hold the work firmly in place, said work supporting member having other portions of relatively low permeability, and means for effecting relative movement between the work supporting member and the magnet, whereby to interpose the portions of relatively low permeability in the aforesaid magnetic circuit and position the portions of relatively high permeability in substantially bridged relation to the poles of the magnet, thereby establishing an auxiliary circuit for releasing the work by diversion of the magnetic flux from the work while the work remains in the normal magnetic work holding zone.

10. A magnetic chuck, comprising a normally open magnetic circuit including flux establishing means, said circuit being adapted to be closed by the work to be held so that the magnetic flux passes through the work and serves to maintain the work firmly in position upon said chuck for operation thereupon, and means including a portion of said magnetic circuit for establishing an auxiliary magnetic circuit exclusive of said work,

whereby to release the work while the work remains in the normal work holding zone.

11. A work holder of the class described comprising a plurality of permanent magnets having poles of opposite polarity disposed adjacent one to another. a casing for said magnets and within which the magnets are slidably mounted, the upper side of said casing forming a work supporting surface and being composed of a material of relatively low permeability and having members of relatively high permeability extending therethrough, said latter members being adapted to register with the poles of said magnets when the magnets are in one position, whereby to aiiord a normally open path for the magnetic lines of flux, which path is adapted to be closed by the work when positioned on the work holding surface within the zone of magnetic influence, and

said members being adapted to substantially bridge poles having opposite polarity when the magnets are shifted to another position, whereby to establish an auxiliary circuit to shunt the magnetic fluxfrom the work-piece while the work remains in the normal magnetic work holding me.

12. A work holder of the class described comprising a plurality of bar magnets arranged in spaced relation to each other, the poles of said magnets being alternately of opposite polarity, a casing within which said magnets are movably mounted and including surfaces contiguous to the opposite ends of said bars, forming work holding surfaces, said work holding surfaces having pole pieces mounted therein for cooperating with the ends of said magnets, the pole pieces of one work supporting surface being displaced relatively to the pole pieces of the other work supll sprain porting surface whereby only one of said work supporting surfaces at a time is rendered operative for holding the work, and means for effecting relative movement between said magnets and said work holding surfaces for selectively registering the pole pieces with the magnets to hold the work on said work supporting surfaces and substantially bridge the poles of opposite polarity to release the work while the work remains in the normal magnetic work holding zone.

13. The method of holding and releasing articles of magnetic material adapted to have work performed thereon, which comprises establishing a closed magnetic circuit in which the magnetic lines of force pass through the work to hold the same, and establishing an auxiliary circuit for shunting magnetic lines of force from said work while the work remains in the normal magnetic work holding zone to release the work.

14. A work holder of the class described, comprising a permanent magnet, pole piece means associated with the poles of said magnet whereby to create a magnetic work holding circuit, and means for effecting relative movement between said pole piece means and magnet to establish an auxiliary circuit for shunting the held out of the work while the work remains in the normal magnetic work holding zone to release the work from said holder without moving the work respecting its held position on the holder.

WILLIAM LESLIE BOWER 

